1. Field of the Invention
The present invention is directed toward stamping presses and, more particularly, toward a method and apparatus for simulating stamping press operation.
2. Description of the Related Art
A stamping press is used to form parts using a large application of force. Stamping is typically used to form metal parts, such as vehicle body panels, from sheet metal. A stamping die set is held in the stamping press, and typically includes a fixed die and a moving die or punch. The fixed die remains stationary on a bottom section of the stamping press. The punch is maintained above while the press is in an open position. A sheet metal blank is placed on the fixed die. A ram drives the punch against the blank and toward the fixed die, thereby forming the blank into a shape of the die set.
It is advantageous to incorporate one or more secondary mechanical devices into at least one of the dies. These devices are beneficial for part handling and for custom-forming specific features into the stamped product. Four basic types of mechanical devices are used in vehicle body panel die blocks. A drop cam is used to form side panels. A cam slider shifts forward in the lower die to eject a formed part. A scrap kicker cuts the trimmings off the edges of the die and kicks them down a chute to be recycled. And a panel lifter pushes the stamped part to permit the part to be lifted out of the die. It is appreciated that some dies for some operations can include three or fewer mechanical devices, depending on the stamping operation.
The timing of operation of the mechanical devices is crucial. For example, if a mechanical device activates before the punch finishes its stroke, misalignment of the stamped part may result, and therefore cause scrapped parts. Also, such misalignment can result in damage to the mechanical devices and/or the die set. The same sort of damage can result if the punch retracts before the mechanical device completes its stroke.
The actuations of the main punch and any secondary devices can be expressed as a function of “rotational angle”. It is to be appreciated that “rotation” corresponds to a single die movement cycle of 360 degrees. The rotational angle of the mechanical devices corresponds to an associated actuation timing within a stamping cycle. FIG. 6A shows rotational angles corresponding to normal operation of a stamping press having a main punch and a secondary mechanical device. As indicated, a punch operation 10a is actuated or advanced at a rotational angle of 240 degrees and retracted at a rotational angle of 330 degrees in a stamping cycle. A mechanical device operation 12a is actuated at 260 degrees in the cycle, after the punch has engaged the material. The mechanical device operation 12a is retracted just before 330 degrees in the cycle, so that the mechanical device will not interfere with retraction of the punch.
However, upon setting up a new die set, or when an existing die set undergoes routine servicing, it is common to experience timing issues with the presses that result in the rotational angles of the various die actuations being out of phase. During servicing, the entire die set may be disassembled, and the pneumatic lines may be disconnected and reconnected. The existing test units for confirming stamp die operation after maintenance include a manually operated hand valve that only allows one mechanical device to be operated at a time. Also, each device must be tested at the repair area pressure and volume, irrespective of its online operation pressure and volume. This introduces errors into the mechanical devices, resulting in changes to their timing, i.e. their effective rotational angles of operation.
As shown in FIG. 6B, the punch operation 10b may be out of phase five degrees ahead of normal (i.e., five degrees leading), actuating at a rotational angle of about 235 degrees and retracting at about 325 degrees. Meanwhile, the mechanical device operation 12b may be out of phase five degrees behind normal (i.e., five degrees lagging), actuating at about 265 degrees and retracting at about 335 degrees. As seen from the figure, the mechanical device would still be extended while the punch is retracting, and may result in the die set hanging up during retraction, which could damage the part and any of the interfering die components.